The present invention relates to a bubble generator or aeration apparatus. More particularly, this invention relates to a bubble generator for aerating septic tank waste water that can produce substantial amount of micro scale air bubbles with a simple rotating mechanism that consumes minimal energy.
An aeration apparatus is used to produce gas bubbles in liquid. In a septic tank, an aeration apparatus is to supply oxygen in the waster water in the tank to promote decomposition of organic sludge by aerobic bacteria.
U.S. Pat. Nos. 5,194,144, 5,951,867 and 6,245,237 disclose an aeration apparatus for septic tanks. Air enters the upper end of a shaft and exits adjacent a propeller. The propeller rotates in the waste water. With high speed rotation of the propeller, air is moved from the atmosphere along the shaft and injected into the water as tiny air bubbles. The aeration apparatus agitates water with the propeller to produce air bubbles and move the produced air bubbles. Large energy was needed to rotate the propeller and the rotation of the propeller to agitate the water caused vibration of the parts rotating the propeller and interference of objects with the propeller and the driving parts.
U.S. Pat. Nos. 6,461,500 and 6,884,353, which are incorporated by reference in this application, disclose an aeration apparatus for septic tanks, which includes an impeller driven by a motor, and an air plate positioned between the impeller and the motor and having a series of concentrically positioned apertures. Air is injected into the waste water through the apertures of the air plate as the impeller is rotated by the motor. Air bubbles have smaller size, and the movement of water induced by the rotation of the impeller is much smaller compared to the apparatus of U.S. Pat. No. 6,245,237, so that the sludge in the tank is not agitated. The aeration apparatus of U.S. Pat. Nos. 6,461,500 and 6,884,353 has disadvantages that the apertures of the air plate are plugged easily; it is hard to balance the impeller and resulting vibration ruins the motor; and there is limit on pitch of the impeller for greater negative pressure.
The efficiency of aeration apparatus is closely related to the number and size of air bubbles that the apparatus produces. The smaller the size of bubbles is, the more efficient the aeration apparatus is. Smaller bubbles stay longer in the water, are easier to be dispersed by Brownian movement, and more efficient in transfer of oxygen since they have greater surface are for the same amount of air made into bubbles. There has long been a need to a bubble generator that can produce air bubbles having smaller size.